Coating composition

ABSTRACT

The present invention provides (i) a novel composition which is the polyol reaction product polyol made by mixing together a polyhydroxyl-tertiary amine, at least two of the hydroxyl groups of said amine being indirectly bonded to a nitrogen atom of said amine through a chain containing at least two carbon atoms, with an organic polyisocyanate, essentially all the isocyanate groups of said polyisocyanate being reacted with hydroxyl groups of said amine, and (ii) a coating composition containing a film forming binder and a volatile organic liquid carrier, said binder containing (I) hydroxyl-containing acrylic polymer and (II) the novel composition (i).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to coating compositions which are especiallyuseful for clear coating over a colored base coat.

2. Description of Related Art

U.S. Pat. No. 5,279,862 discloses a clear coating composition which canbe used as the clear coat of a motorized vehicle clear coat/color coatfinish. The clear coating composition has a film-forming binder andvolitile organic liquid carrier, the binder including hydroxy functionalacrylic polymer and organic polyisocyanate and is characterized by rapidcuring to form a finish that is tack free and can be buffed as soon as3-4 hours after application, resulting in increased productivity of thepaint shop.

Even more rapid curing of the clear coat is desired for further increasein paint shop productivity. A catalyst for the hydroxy-isocyanatecrosslinking reaction is present in the clear coating composition,typically an organo tin compound. When the amount of catalyst isincreased to speed-up the cure, other problems arise, includingdecreased potlife and reduced coating quality. In the latter case, thefaster cure entraps liquid carrier within the dried clear coating,causing the coating to have poor gloss and distinctness of image.

There are other indicia of increased productivity, e.g. how soon afterapplication the film coating dries sufficiently to be dust-free, so thatthe painted article (vehicle) can be moved from the paint booth, to makeroom for the next vehicle to be painted. The vehicle can be movedoutside the paint shop, i.e. into the open air, only after the filmcoating has dried further so as to be free of water spotting damage.

SUMMARY OF THE INVENTION

The present invention provides (a) a coating composition which formsfilm coatings which provide improved productivity as determined by oneor more of the indicia of rapidly becoming dust-free and water spotresistant, and/or rapid curing sufficiently to be buffed, all occuringat ambient temperature (20° C.), (b) a novel binder component for use in(a), and (c) a novel ingredient for use in (b). The coating composition(a) of the present invention contains a film forming binder and avolatile organic liquid carrier binder, wherein the binder contains

(A) hydroxyl-containing acrylic polymer and polyol prepared by reactingtogether polyhydroxyl-tertiary amine with organic polyisocyanate, thepolyhydroxyl-tertiary amine having at least two hydroxyl groups beingindirectly bonded to a nitrogen atom of said amine through a chaincontaining at least two carbon atoms, essentially all of the isocyanategroups of said organic polyisocyanate being reacted with hydroxyl groupsof said amine,

(B) organic polyisocyanate, the ratio of equivalents of isocyanate in(B) per equivalent of hydroxyl groups in (A) being in the range of 0.5/1to 3.0/1, and

(C) an effective amount of catalyst to cure said composition.

The novel binder component (b) of the present invention is thecombination of the hydroxyl-containing acrylic polymer and polyoldescribed as component (A) above, preferably also contained in avolatile organic liquid carrier, the combination of thehydroxyl-containing acrylic polymer and the polyol also constituting afilm-forming binder. Components (A) and (B) are packaged separately andare combined just prior to application, because component (B) crosslinksthe combined components. Component (C) speeds up the crosslinkingreaction and can be provided to the crosslinking reaction either as partof (A), (B), or as a separate component. In any event, the pot-life ofthe combined components is sufficient to enable the combined componentsto be applied, typically by spraying, onto the substrate to be coated,typically an vehicle body part, including the entire vehicle body.

The curing of the composition after it is applied to form the filmcoating occurs by the isocyanate groups of (B) reacting with thehydroxyl groups of both the acrylic polymer and the polyol of (A) toform urethane linkages, whereby the cured coating film is apolyurethane. The polyol both speeds up the curing reaction, as does thecatalyst (C), and becomes part of the crosslinked structure by thereaction of its hydroxyl groups with the isocyanate groups. Thus, thepolyol is present in an effective amount to increase the crosslinkingreaction rate during curing of the composition. Preferably, the amountof said acrylic polymer is 40-99 wt % and the amount of polyol is 1-60wt %, based on the total weight of (A).

The novel ingredient (c) of the present invention is the polyol ofcomponent (A). It is desirable that the polyol is essentally free ofisocyanate groups so that there will be no appreciable reaction betweenthe polyol and the hydroxyl-containing acrylic polymer when theseingredients are combined into component (A), otherwise there would bepremature crosslinking of component (A) that would interfere with theapplication of the coating composition such as by spraying and wouldgive a defective coating, if sprayable at all. The reaction between thepolyhydroxyl-tertiary amine and the polyisocyanate to form the polyol ofcomponent (A) is spontaneous, i.e. it occurs merely by mixing theseingredients together at ambient temperature and under atmosphericpressure. The polyol reaction product is a mixture of reaction productsin which different number of molecules of the amine react with a singlemolecule of the poyisocyanate and in which one molecule of the amine mayreact with a plurality of molecules of the polyisocyanate. The fact thatessentially all of the isocyanate groups of the polyisocyanate are usedup in the reaction and that the reaction product is a polyol indicatesthat an excess of hydroxyl groups provided by the polyhydroxyl-tertiaryamine is present in the reaction. These hydroxyl groups in the polyolbear the same relationship to the amine nitrogen as in thepolyhydroxl-tertiary amine reactant.

Film coatings formed from compositions (a) of the present inventiontypically become dust-free within 10 min and even within 5 min, free ofwater spot damage within 30 min, and can be buffed in less than threehours and possibly as early as one hour after application, all withambient temperature drying and cure, without sacrifice in either theease of applying the coating composition or the ultimate quality of theclear coat. Of course, the film coating becomes tack-free prior tobecoming buffable. Thus, the coating compositions of the presentinvention are highly useful for repairing a clearcoat/colorcoat finishof a vehicle using the coating composition as a refinish clearcoat,which process allows the vehicle to be moved outside and the finish tobe sanded (wet or dry), buffed or polished, if necessary, to removeminor imperfections and enhance gloss within a short period of timeafter application. This greatly improves the productivity of a refinishoperation by allowing more vehicles to be processed in the same or inless time.

DETAILED DESCRIPTION OF THE INVENTION

The coating composition (a) of this invention is a low VOC (volatileorganic content) composition that is particularly suited for use as aclearcoat in automotive refinishing. The composition contains a filmforming binder and an organic liquid carrier which is usually a solventfor the binder. Since the invention is directed to a low VOCcomposition, the amount of organic solvent used in the liquid carrierportion results in the composition having a VOC content of less than 0.6kilograms per liter (5 pounds per gallon) and preferably in the range ofabout 0.25-0.53 kilograms (2.1-4.4 pounds per gallon) of organic solventper liter of the composition, as determined under the procedure providedin ASTM D-3960.This usually translates to a film forming binder content(components (A)+(B)+(C)) of about 25-90% by weight and an organic liquidcarrier content of about 10-75% by weight, preferably about 30-55% byweight binder and 45-70% by weight carrier. Component (A), by itself canhave the same solids content in organic liquid carrier, with or withoutthe presence of component (C) in component (A). “Solids content” as usedherein refers to the film-forming binder content of the composition,i.e. although the binder is in solution in the carrier, upon evaporationof the carrier, solid coating film of the binder remains,

The hydroxyl functional acrylic polymer used in the hydroxyl componentof the binder is prepared by conventional solution polymerizationtechniques in which monomers, solvents and polymerization catalyst arecharged into a conventional polymerization reactor and heated to about60-200° C. for about 0.5-6 hours to form a polymer having a weightaverage molecular weight (Mw) of preferably about 2,000-13,000, morepreferably about 3,000-11,000.

All molecular weights disclosed herein are determined by GPC (gelpermeation chromatography) using polymethyl methacrylate standard,unless otherwise noted.

The acrylic polymer thus formed also has a glass transistion temperature(Tg) generally of at least 20° C. and preferably about 40-80° C.

All glass transition temperatures disclosed herein are determined by DSC(differential scanning calorimetry).

Typically useful polymerization catalysts are azo type catalysts such asazo-bis-isobutyronitrile, 1,1′-azo-bis(cyanocylohexane), acetates suchas t-butyl peracetate, peroxides such as di-t-butyl peroxide, benzoatessuch as t-butyl perbenzoate, octoates such as t-butyl peroctoate and thelike.

Typical solvents that can be used are ketones such as methyl amylketone, methyl isobutyl ketone, methyl ethyl ketone, aromatichydrocarbons such as toluene, xylene, alkylene carbonates such aspropylene carbonate, n-methyl pyrrolidone, ethers, ester, such as butylacetate, and mixtures of any of the above.

The hydroxyl functional acrylic polymer is preferably composed of amixture of monomers, predominantly (meth)acrylic which copolymerizetogether to provide the application and cured coating filmcharacteristics desired polymerized. In accordance with the presentinvention it is important that the acrylic polymer also contain hydroxylgroups provided by one or more comonomers used to form the acrylicpolymer. The preferred mixture of comonomers is styrene, a methacrylatewhich is either methyl methacrylate, isobomyl methacrylate, cyclohexylmethacrylate or a mixture of these monomers, a second methacrylatemonomer which is either n-butyl methacrylate, isobutyl methacrylate orethyl hexyl methacrylate or a mixture of these monomers and a hydroxyalkyl methacrylate or acrylate that has 1-8 carbon atoms in the alkylgroup such as hydroxy ethyl methacrylate, hydroxy propyl methacrylate,hydroxy butyl methacrylate, hydroxy ethyl acrylate, hydroxy propylacrylate, hydroxy butyl acrylate and the like.

A preferred acrylic polymer contains about 5-30% by weight styrene,1-50% by weight of the methacrylate, 30-60% by weight of the secondmethacrylate and 10-40% by weight of the hydroxy alkyl methacrylate. Thetotal percentage of monomers in the polymer equal 100%. One particularlypreferred acrylic polymer contains the following constituents in theabove percentage ranges: styrene, methyl methacrylate, isobutylmethacrylate and hydroxy ethyl methacrylate. Another preferred acrylicpolymer contains the following constituents in the above percentageranges: styrene, isobomyl methacrylate, ethyl hexyl methacrylate,hydroxy ethyl methacrylate and hydroxy propyl methacrylate. Stillanother preferred acrylic polymer contains the following constituents inthe above percentages: styrene, methyl methacrylate, isobomylmethacrylate, ethyl hexyl methacrylate, isobutyl methacrylate, andhydroxy ethyl methacrylate. Most preferably, compatible blends of two ormore of the above acrylic polymers are used.

Optionally, the acrylic polymer can contain about 0.5-2% by weight,based on the weight of acrylic polymer, of acrylamide or methacrylamidesuch as n-tertiary butyl acrylamide or methacrylamide, copolymerizedwith the acrylic polymer.

The polyol ingredient in component (A) is, as stated above, the reactionproduct obtained by mixing together organic polyisocyanate andpolyhydroxyltertiary amine, with the resultant polyol being present in(A) as a mixture with the acrylic polymer in solution in the liquidcarrier.

With respect to the polyhydroxyl-tertiary amine reactant, its essentialcomponents are the presence of at least one tertiary amine nitrogen atomand a plurality of hydroxyl groups, with at least two of the hydroxylgroups being bonded to at least one of the nitrogen atoms via abifunctional group which contains at least two carbon atoms, i.e. the—OH substitution is no closer than beta to the nitrogen atom. Thisrelationship between —OH groups and amine nitrogen is carried over intothe polyol reaction product. The bifunctional group can be an aliphaticgroup preferably containing 2 to 12 carbon atoms. When the tertiaryamine has two nitrogen atoms, preferably at least one —OH group isindirectly substituted onto each nitrogen atom as described above. Thepolyol is non-reactive with the acrylic polymer and can be used in thecomposition of the present invention as a singlepolyisocyanate/polyhydroxyltertiary amine reaction product or as amixture of different polyisocyanate/polyhydroxyl-tertiary amine reactionproducts.

Polyhydroxyl-tertiary amines that can be used to make the polyol of thepresent invention include those represented by the formula

wherein k is alkylene or oxyalkylene containing 0 to 6 carbon atoms andX and Y are independently R₁H, wherein R₁ is —(CH₂CH₂O)_(n)— or—(CH₂C(CH₃)HO)_(n)—, wherein n is an integer of 1-3, and A is R—X, R—Y,R₂or Z,

wherein R₂ is an alkyl group containing 1-20 carbon atoms and

wherein R₃ is an alkylene group containing 1 to 10 carbon atoms, withthe proviso that at least two, preferably at least three, —OH groups(provided by R₁H) are present. Preferably, R when present is alkylenecontaining 2 to 4 carbon atoms, R₁ is —CH₂CH₂O)_(n)—, wherein n is 1 or2, R₂is an alkyl group containing 1-4 carbon atoms or 8 to 20 carbonatoms, and R₃ is an alkylene group containing 2 to 6 carbon atoms. Thecombination of R and R₁ form one embodiment of aliphatic groupindirectly connecting the —OH group to the nitrogen atom.

Examples of polyhydroxyl-tertiary amines include simple compounds suchas N,N-diethanol alkyl amine, triethanol amine and more complicatedcompounds which can be considered as oligomers, such as the Ethomeen®(one tertiary amine nitrogen atom) and Ethoduomeen® (two tertiary aminenitrogen atoms) compounds available from Akzo Nobel. Examples of thesecompounds in which only one tertiary amine nitrogen is present arerepresented by the formula

wherein R₂, R, X, and Y have the same meaning as described above andwherein R₂ preferably has 8 to 20 carbon atoms. Examples of group R₂ aretallow, oleyl, coco, and soya. A preferred group of compounds are thediethoxylates characterized by the formula

Wherein R₂ contains 8-20 carbon atoms. Examples of compounds containingtwo tertiary amine nitrogen atoms include the Ethoduomeens such as thecompound having the formula

and the compounds having the formula

Wherein m is an integer independently selected from the group 0, 1, or2, and o is an integer of from 1 to 4.

In the Ethomeen® and Ethoduomeen® compounds containing the R₂ group,such group is a mixture of alkyl groups as shown in the following TableA.

TABLE A Approximate Alkyl Wt. % Distribution Hydrogenated Alkyl DecylDodecyl Hexadecyl Octadecyl Oleyl Oleyl Coco Soya Tallow TallowSaturated C8 4 6 C10 90 1 7 C12 6 95 0.5 0.5 51 0.5 C14 3 1.5 1.5 19 1 33.5 C15 0.5 0.5 0.5 C16 1 91 9 4 4 9 16 29 31 C17 1.5 2 0.5 0.5 1 1 C187 87 14 8 2 15 20 61 Unsaturated C14′ 0.5 0.5 0.5 C16′ 4 4 1 2 C18′ 2 7074 6 49.5 44 3 C18″ 5 7 13

The organic polyisocyanate reactant to make the polyol of the presentinvention can be a single polyisocyanate or a blend of differentpolyisocyanates and can be represented by the formula

wherein B is an aliphatic or aromatic nucleus of the polyisocyanate andp is an integer of at least 2.Generally, p will be an integer of nogreater than 6.

Any of the conventional aromatic and aliphatic diisocyanates,trifunctional isocyanates and isocyanate functional addition compoundsof a polyol and a diisocyanate may be used as the reactant to make thepolyol of the present invention. The aliphatic polyisocyanate can becycloaliphatic.

From the following, it will be seen that nuclei B can have a widevariety of identities. Typically useful diisocyanates are1,6-hexamethylene diisocyanate, isophorone diisocyanate,4,4′-biphenylene diisocyanate, toluene diisocyanate, bis cyclohexyldiisocyanate, tetramethylene xylene diisocyanate, ethyl ethylenediisocyanate, 2,3-dimethyl ethylene diisocyanate, 1-methyltrimethylenediisocyanate, 1,3-cyclopentylene diisocyanate, 1,4-cyclohexylenediisocyanate, 1,3-phenylene diisocyanate, 1,5-naphthalene diisocyanate,bis(4-isocyanatocyclohexyl)-methane, 4,4′-diisocyanatodiphenyl ether andthe like.

Typical trifunctional isocyanates that can be used are triphenylmethanetriisocyanate, 1,3,5-benzene triisocyanate, 2,4,6-toluene triisocyanateand the like. Trimers of other diisocyanates also can be used such asthe trimer of hexamethylene diisocyanate (HDI) which is sold under thetradename “Desmodur” N-3300 or N-3390 or “Tolonate” HDT or HDT-LV.Trimer of isophorone diisocyanate (IPDI) can also be used. In formingthe trimer from isophorone diisocyanate, one of the isocyanate groupsforms an isocyanurate group; the resultant trimer, however, has threeisocyanate groups. Typically useful IPDI trimers are sold under thetradenames “Desmodur” Z-4470 BA or SN/BA or SN or MPA/X. The IPDI trimeroffers the resulting coating improved hardness on curing.

Isocyanate functional addition compounds can also be used that areformed from an organic polyisocyanate and a polyol (the reaction formingthe addition compound uses up the —OH groups of the polyol). Any of theaforementioned polyisocyanates can be used with a polyol to form anaddition compound. Polyols such as trimethylol alkanes like trimethylolpropane or ethane can be used. One useful adduct is the reaction productof tetramethylxylidene diisocyanate and trimethylol propane and is soldunder the tradename “Cythane” 3160.

The reaction between the polyisocyanate and the polyhydroxyl-tertiaryamine occurs merely by mixing these ingredients together such as atambient temperature and atmosphereric pressure, although it is preferredto carry out the reaction in an inert atmosphere, such as under anitrogen blanket. It is preferred that the reaction occurs by onemolecule of the polyhydroxyl-tertiary amine reacting with only oneisocyanate group of the polyisocyanate, whereby the polyol reactionproduct can be represented by the formula

wherein A, B, Y, R, R₁ and p have the same meaning as stated above. Thereaction favors the formation of this reaction product if in the courseof mixing the reactants together, the amine reactant is maintained in anexcess amount (molecules of amine vs. molecules of polyisocyanate),whereby the overall reaction product will contain at least 50 mol % ofthis favored reaction product. The amine reactant can be maintained inexcess by slowly adding the polyisocyanate reactant to a solution of thepolyhydroxyl-tertiary amine reactant and letting the resultant reactionstand for a period of time to allow essentially all of the isocyanategroups to react. The slow addition can be dropwise addition. Preferably,the polyisocyanate addition is carried out at a rate of not more than 20wt %/min, and more preferably, not more than 10 wt %/min until 100 wt %of the polyisocyanate is added to the amine reactant. Even under thisslow addition processs, one molecule of the polyhydroxyl-tertiary aminecan add to multiple isocyanate groups of the same molecule ofpolyisocyanate reactant to form the reaction product represented by theformula

wherein B has the same meaning as above. It is even possible for thehydroxyl groups of one molecule of polyhydroxyl-tertiary amine to reactwith isocyanate groups of different molecules of the polyisocyanatereactant.

The combination of the hydroxyl-containing acrylic polymer and thepolyol of the present invention (component (A)) crosslinked with thepolyisocyanate (component (B)) to be described hereinafter produces aclear, tough glossy film coating. The proportions of the acrylic polymerand polyol required to produce this result, along with quick curing willdepend on the particular acrylic polymer and polyol selected, and tosome extent on the particular polyisocyanate selected as component (B).Preferably, however, an effective amount of the polyol of the presentinvention will be present to reduce the curing time so that water spotdamage does not occur after one hour after application of the coating,followed by drying at ambient temperature (20° C.). Typically, theamount of the polyol needed to achieve this goal will be from 1 to 20 wt% of component (A).

Component (A) can further contain a hydroxyl- terminated polyester suchas that having a weight average molecular weight (Mw) not exceedingabout 3,000 (oligomer), preferably about 200-2,000, and a polydispersity(Mw divided by Mn) of less than about 1.7.

Typically useful such oligomers include caprolactone oligomerscontaining terminal hydroxyl groups which may be prepared by initiatingthe polymerization of caprolactone with a cyclic polyol, particularly acycloaliphatic polyol, in the presence of a tin catalysts viaconventional solution polymerization techniques. Such caprolactoneoligomers are well known and described at length in Anderson et al. U.S.Pat. No. 5,354,797, issued Oct. 11, 1994.Epsilon(ε)-caprolactone istypically employed as the caprolactone component in a 1/1 to 5/1 molarratio with a cycloaliphatic diol. Typically useful cycloaliphatic polyolmonomers include 1,4-cyclohexanediol, 1,4-cyclohexane dimethanol, and2,2′-bis(4-hydroxycyclohexyl) propane. Preferred caprolactone oligomersare formed from—caprolactone and 1,4-cyclohexanedimethanol reacted in amolar ratio of 2/1 to 3/1.

Other useful oligomers include alkylene oxide polyester oligomerscontaining terminal hydroxyl groups which may be made by reactingstoichiometric amounts of a cycloaliphatic monomeric anhydride with alinear or branched polyol in solution at elevated temperatures in thepresence of a tin catalyst using standard techniques and then cappingthe acid oligomers so formed with monofunctional epoxies, particularlyalkylene oxide, under pressure above atmospheric but not exceeding about200 psi and at temperatures of 60-200° C. for 1 to 24 hours. Suchalkylene oxide oligomers are well known and described at length inBarsotti et al. PCT Application No. U.S. Ser. No. 98/23337, publishedMay 14, 1999.

Cycloaliphatic anhydride monomers such as hexahydrophthalic anhydrideand methyl hexahydrophthalic anhydride are typically employed in thealkylene oxide oligomers above. Aliphatic or aromatic anhydrides, suchas succinic anhydride or phthalic anhydride may also be used inconjunction with the anhydrides described above. Typically useful linearor branched polyols include, hexanediol, 1,4-cyclohexane dimethanol,trimethylol propane, and pentaerythritol. Useful monofunctional epoxiesinclude alkylene oxides of 2 to 12 carbon atoms. Ethylene, propylene andbutylene oxides are preferred although ethylene oxide is most preferred.Other epoxies, such as “Cardura” E-5 or “Cardura” E-10 glycidyl ether,supplied by Exxon Chemicals, may be used in conjunction with themonofunctional epoxies described above. Particularly preferred alkyleneoxide oligomers are formed from methyl hexahydrophthalic anhydride;either 1,4-cyclohexanedimethanol, trimethylol propane, orpentaerythritol; and ethylene oxide reacted in stoichiometric amounts.

Compatible blends of any of the aforementioned hydroxyl-terminatedpolyesters can be used as well in the hydroxyl component (A) of thebinder. Generally, 0 to 39 wt %, based on the total weight of component(A) of the hydroxyl-terminated polyester will be present, and preferablythe amount will be 1 to 20 wt %.

The polyisocyanate component (B) of the binder coating compositionincludes an organic polyisocyanate as the crosslinking agent. Theorganic polyisocyanate can be a single polyisocyanate or a blend ofdifferent polyisocyanates.

Any of the conventional aromatic, aliphatic, cycloaliphaticdiisocyanates, trifunctional isocyanates and isocyanate functionaladdition compounds of a polyol and a diisocyanate may be used as or inthe polyisocyanate component (B).

Typical useful diisocyanates, triisocyanates and isocyanate functionaladdition compounds that can be used in component (B) are the same asdisclosed above as reactants with the polyhydroxyl-tertiary amine toform the polyol of the present invention. Just as in the case of formingthe polyol of the present invention, when the polyisocyanate used incomponent B contains IPDI trimer, the resulting coating exhibitsimproved hardness on curing. Thus IPDI trimer can be incorporated intothe coating composition either by the polyol of the present invention incomponent (A) or as part of component (B) or by both.

In the present invention, the polyisocyanate component (B) contains 0%,but preferably at least 3% up to about 50% by weight, more preferablyabout 5-30% by weight, of the IPDI trimer, based on the weight ofcomponent (B). Excessive IPDI trimer tends to cause the film coating tobecome too brittle, whereby the coating film will crack over time.

One particularly preferred polyisocyanate crosslinking componentcomprises a mixture of about 5-45% by weight IPDI trimer and about55-95% by weight HDI trimer, based on the total weight of component (B).The preferred amount of IPDI trimer for use in combination with HDItrimer is 5 to 30 wt %. It is generally preferred to employ an HDItrimer in combination with the IPDI trimer to retain flexibility in thecoating film.

The hydroxyl and polyisocyanate components (A) and (B), respectively arepreferably employed in an equivalent ratio of isocyanate groups tohydroxyl groups of 0.8/1 to 2.0/1.

The coating composition also contains a sufficient amount of catalyst(component (C)) to cure the composition at ambient temperature. Acombination of certain catalysts is preferred when IPDI trimer ispresent, to accelerate the curing rate of IPDI trimer at roomtemperature to achieve the high film hardness offered by IPDI in arelatively short period of time, with little or no pot life reductionsor die-back in the coating film formed therefrom. Even at theseaccelerated curing rates, the coating compositions remains processablefor at least 30 minutes at ambient temperatures which provides enoughtime to complete the refinish job without the need for viscosityadjustments, and the high gloss coating film formed therefrom showsvirtually no signs of dying back to a dull fuzzy finish over time.

The catalyst comprises at least one organotin tin compound, optionallyat least one tertiary amine, and optionally, at least one organic acidin amounts described below (catalyst system).

Typically useful organotin compounds include organotin carboxylates,particularly dialkyl tin carboxylates of aliphatic carboxylic acids,such as dibutyl tin dilaurate (DBTDL), dibutyl tin dioctoate, dibutyltin diacetate, and the like. Although not preferred, any of the othercustomary organotin or organometallic (Zn, Cd, Pb) catalysts could alsobe used. The amount of organotin catalyst employed in the coatingcomposition can vary considerably depending on the specific bindersystem and the degree of initial hardness desired. However, it iscritical that the coating composition contains enough organotin catalystto cure the composition at ambient temperatures, while at the same timebeing insufficient to cause die-back.

Generally, about 0.005-0.2% by weight, based on the weight of the binder(components (A)+(B)+(C)), of organotin catalyst will be sufficient toimpart the desired properties. It has been found that above the upperlimit of 0.2%, the curing reaction is too fast and die-back results.Below about 0.005%, the curing reaction is too slow and insufficienthardness and poor mechanical properties develop. The organotin catalystcan be used by itself as the sole catalyst ingredient.

Typically useful tertiary amines useful as a co-catalyst in catalystcomponent (C), as distinguished from the polyhydroxyl-tertiary amineused to form the polyol in component (A), include tertiary aliphaticmonoamines or diamines, particularly trialkylene diamines, such astriethylene diamine (DABCO), N-alkyl trimethylenediamine, such asN,N,N′-trimethyl-N′-tallow- 1,3-diaminopropane, and the like; andtrialkylamines such as tridodecylamine, trihexadecylamine,N,N′-dimethylalkyl amine, such as N, N′-dimethyldodecyl amine, and thelike, all free of —OH groups. The alkyl or alkylene portions of theseamines may be linear or branched and may contain 1-20 carbon atoms.Especially preferred are amines that contain at least 6 carbon atoms inat least one of their alkyl or alkylene portions to lower the hazing inhumid conditions.

As with the amount of organotin compound, the amount of tertiary aminein the catalyst system employed in the coating composition can varyconsiderably, it being desired only that tertiary amine if present, bepresent in an amount which, together with the above, including component(A), will cause the composition to cure (sufficient for buffability) atambient temperature within three hours, preferably within two hours.Generally, about 0.01-1% by weight, based on the weight of the binder,of tertiary amine will be sufficient to impart the desired properties.Above the upper limit of about 1%, the tertiary amine offers longer dustdrying times and provides the film with insufficient hardness. Belowabout 0.01%, the catalytic effect is generally inadequate.

An organic acid is also included in the catalyst system for increasedpot life.

A pot life of at least 30 minutes at ambient temperatures is generallysufficient for completion of a refinish job. Typically useful acidcatalysts are formic acid, acetic acid, proponic acid, butanoic acid,hexanoic acid, and any other aliphatic carboxylic acid, and the like.Generally, about 0.005-1%, based on the weight of the binder, of acid isemployed.

It has been found that the three-component catalyst system describedabove offers a higher cure response than organotin, amine, or acidalone.

To improve weatherability of the composition about 0.1-10% by weight,based on the weight of the binder, of ultraviolet light stabilizersscreeners, quenchers and antioxidants can be added. Typical ultravioletlight screeners and stabilizers include the following:

Benzophenones such as hydroxy dodecyloxy benzophenone, 2,4-dihydroxybenzophenone, hydroxy benzophenones containing sulfonic acid groups andthe like.

Benzoates such as dibenzoate of diphenylol propane, tertiary butylbenzoate of diphenylol propane and the like.

Triazines such as 3,5-dialkyl-4-hydroxyphenyl derivatives of triazine,sulfur containing derivatives of dialkyl-4-hydroxy phenyl triazine,hydroxy phenyl-1,3,5-triazine and the like.

Triazoles such as 2-phenyl-4-(2,2′-dihydroxy benzoyl)-triazole,substituted benzotriazoles such as hydroxy-phenyltriazole and the like.

Hindered amines such as bis(1,2,2,6,6 entamethyl-4-piperidinylsebacate), di[4(2,2,6,6, tetramethyl piperidinyl)]sebacate and the likeand any mixtures of any of the above.

Generally, flow control agents are used in the composition in amounts ofabout 0.01-5% by weight, based on the weight of the binder, such aspolyacrylic acid, polyalkylacrylates, polyether modified dimethylpolysiloxane copolymer and polyester modified polydimethyl siloxane.

When used as a clear coating, it may be desirable to use pigments in theclear coating composition which have the same refractive index as thedried coating. Typically, useful pigments have a particle size of about0.015-50 microns and are used in a pigment to binder weight ratio ofabout 1:100 to 10:100 and are inorganic siliceous pigments such assilica pigment having a refractive index of about 1.4-1.6.

The coating composition of the present invention also contains thecustomary organic solvents in the organic liquid carrier portion. Aspreviously described, the amount of organic solvent(s) added dependsupon the desired binder level as well as the desired amount of VOC ofthe composition. Typical organic solvents consist of aromatichydrocarbons, such as petroleum naphtha or xylenes; ketones, such asmethyl amyl ketone, methyl isobutyl ketone, methyl ethyl ketone, oracetone; esters, such as butyl acetate or hexyl acetate; and glycolether esters, such as propylene glycol monomethyl ether acetate.Examples of solvents which do not contribute to the VOC of thecomposition include methyl acetate, acetone, 1-chloro, 4-trifluoromethylbenzene, and potentially t-butyl acetate.

The coating composition of this invention is preferably prepared as a“two-component” or “two-pack” coating composition, wherein the tworeactive binder components (A) and (B) are stored in separatecontainers, which are typically sealed. The catalyst (component (C),organic solvent, and usual other additives may be added to either orboth the hydroxyl or crosslinking components, depending upon theintended use of the composition. However, these additives (except forsome solvent) are preferably added to and stored in the same containerwith the hydroxyl component (A). The contents of the hydroxyl andisocyanate component containers are mixed in the desired NCO/OH ratiojust prior to use to form the activated coating composition, which has alimited pot life. Mixing is usually accomplished simply by stirring atroom temperature just before application. The coating composition isthen applied as a layer of desired thickness on a substrate surface,such as an autobody part, including the entire autobody. Afterapplication, the layer dries and cures to form a coating on thesubstrate surface having the desired coating properties.

Generally, the coating composition of this invention is used as aclearcoat in automotive refinishing, but it should be understood that itcan also be used as a clearcoat finish or can be pigmented withconventional pigments and used as a monocoat or as a basecoat in aclearcoat/colorcoat finish or refinish.

In the application of the coating composition as a clearcoat refinish toa vehicle part such as an automobile or a truck body or portion thereof,the basecoat which may be either a solvent based composition or awaterborne composition is first applied and then dried sufficiently toform a stable basecoat for the clear coat before the clearcoat isapplied usually wet-on-wet by conventional spraying. Electrostaticspraying also may be used. In refinish applications, the composition ispreferably dried and cured at ambient temperatures but can be forceddried and cured in paint booths equipped with heat sources at slightlyelevated booth temperatures of, in general, about 30-100° C., preferablyabout 35-65° C., for a short time of about 3-30 minutes, preferablyabout 5-15 minutes. The coating so formed is typically about 0.5-5 mils(0.012 to 0.12 mm) thick.

In these refinish applications, in particular, the clearcoat of thisinvention has been found to greatly improve the productivity of arefinish operation. Through incorporation of a mixture ofhydroxy-containing polyacrylic resin, polyol of the present invention,polyisocyanate, preferably containing some IPDI trimer, and effectivecatalysts, the composition when used as a clearcoat dries and cures in arelatively short time after application to a dust free, water resistant,and sufficiently hard state for sanding (wet or dry) or buffing,unexpectedly with minimum pot life reductions and without die-backconsequences, which allows the vehicle to be buffed, moved out of theway, and delivered to the customer on the same day of application, incomparison to the next day offered by conventional clear coatcompositions. The composition of this invention, in particular, exhibitsa pot life of at least 30 minutes at ambient temperature, dust free timewithin 10 minutes or less at ambient temperatures, and water spot freeand wet sand or buff time within 3 hours, preferably within 2 hours, andeven as soon as one hour, at ambient temperatures. The foregoingproperties can be achieved much faster by curing the composition atslightly elevated temperatures of, in general, about 55-65° C. peaksubstrate temperature for about 3-10 minutes, and preferably about 60°C. for about 6 minutes, which remarkably allows the clear finish to besanded or buffed immediately on cool down. Furthermore, the finishremains sandable or buffable for several days up to one week before itcures to a tough, hard durable exterior automotive finish.

The coating composition of this invention can be used to paint or repaira variety of substrates such as previously painted metal substrates,cold roll steel, steel coated with conventional primers such aselectrodeposition primers, alkyd resin repair primers and the like,plastic type substrates such as polyester reinforced fiber glass,thermoplastic olefin (TPO), reaction injection molded urethanes andpartially crystalline polyamides, as well as wood and aluminumsubstrates.

EXAMPLES

Test Procedures

The following test methods were used to evaluate the coatings:

The film hardness is another indication of when the coating film isready to be sanded, buffed or polished. The coating film alone must havea Persoz hardness of at least 35 sec. (counts), preferably in the rangeof about 40-150 counts, at a film thickness of 2.2 mils when measured ona previously uncoated cold rolled steel (Q) panel before it can besanded, buffed or polished, and this is the criterion and testconditions used in the Examples. Persoz hardness is determined by aGARDCO® Pendulum Hardness Tester Model HA-5854 manufactured by BYKChemie, Germany and sold by Paul N. Gardness Company, Inc. PompanoBeach, Fla.

The coating must also be water spot free before it is ready to be wetsanded or stored in the rain. If water spot damage is formed on thefilm, this is an indication that the cure is not complete and furthercuring is needed before the film can be wet sanded or exposed to rainyweather conditions. The water spot free time was determined by putting awater drop on the refinish film for every 15 min. and up to 24 hours.The water will damage the film if it is not cured. As a consequence, thewater drop will form a damage ring on the refinish panel. The degree ofdamage is rate from 1 to 10 scale. A score of 10 indicates no damagewhile 1 indicates severe water spotting.

The die-back was determined visually by one skilled in the art. Oneskilled in the art compares the initial gloss and DOI (distinctness ofimage) of the coating film with the gloss and DOI after the film isallowed to dry overnight. If there is a significant drop in the glossand DOI levels, such that the coating film has a dull fuzzy appearance,die-back is said to result.

Example 1

Hydroxyl-containing acrylic polymer (acrylic polymer 1) was prepared bycharging the following constituents into a polymerization reactorequipped with a heating mantel, a stirrer, thermometer, addition funnel,nitrogen purge and reflux condenser.

Parts By Weight Portion 1 Xylene 56 Portion 2 Methyl ethyl ketone 10Styrene monomer 15 Isobutyl methacrylate monomer 45 Methyl methacrylatemonomer 20 Hydroxy ethyl methacrylate monomer 20 Portion 3 T-butylperacetate solution (75% solids 3.0 in mineral spirits) Total 170

Portion 1 was added to the reactor and heated to its reflux temperature.Portions 2 and 3 were then added together at a uniform rate to thereactor over a three hour period while the resulting reaction mixturewas maintained at its reflux temperature. The reaction mixture was heldat reflux for an additional hour. The resulting acrylic polymer solutionhad a polymer solids content of about 60%. The polymer had a weightaverage molecular weight (Mw) of about 10,500 and a glass transitiontemperature (Tg) of about 58° C.

A tetrahydroxyl-terminated polyester oligomer (oligomer 1) was preparedby charging the following constituents into a high pressure reactionvessel and heated to 140° C.

Ingredients Weight (grams) Propylene glycol monoethyl ether acetate 240Pentaerythritol 136 Triethylamine 0.23

To the reaction vessel, 645 gm of methylhexahydrophthalic anhydride wasthen added over one hour. The batch was held at 140° C. for 6 hr. Thebatch was then cooled to 25° C., the reaction vessel was then sealed,and 173 gm of ethylene oxide was added, followed by heating the batch to110° C. and holding at that temperature for 6 hr. Excess ethylene oxidewas then removed by purging the batch with nitrogen. The acid number ofthe resultant oligomer (solids) was 10 mg KOH/gm. The resulting solutionof oligomer 1 had an 80% by wt. solids content. The oligomer wastetrahydroxyl-substituted and these were all primary functionalities.The oligomer also had a Mw of about 1,000, a Tg of about 0° C., and apolydispersity (Pd) of about 1.1.

The polyhydroxyl-tertiary amine used in this Example was triethoxylatedN-tallow-1,3-diaminopropane available as Ethoduomeen® T/13 by Akzo NobelCo. It has 3 hydroxyl groups and 2 tertiary amines. For simplicity, thisis called oligomer 2.

A polyol of the present invention was prepared from oligomer 2 and IPDItrimer, as follows: At ambient temperature, to a one quart reactionvessel equipped with a mechanical stirrer, was added 124 g of oligomer 2and 53.1 g of butyl acetate. 89.9 g of IPDI trimer (70 wt % solids inbutyl acetate), available as Desmodur® Z-4470 BA, was then slowly addedto the reaction vessel, i.e, the addition was carried out substantiallyuniformly over a fifteen min. period. The contents of the reactionvessel was stirred during this addition and for two hr. thereafter undernitrogen blanket. The reaction vessel was then left stand for 7 days tocomplete the reaction, i.e. all of the isocyanate groups of the IPDIwere reacted with at least one of the hydroxyl groups of oligomer 2,leaving excess hydroxyl groups as the terminal groups of the compound,i.e. the polyol. The polyol is called oligomer 3 in this Example.Oligomer 3 was an inseparable mixture of reaction product in whichmolecules of oligomer 2 were reacted with the IPDI trimer through one,two, and three hydroxyl groups of the oligomer 2, although about 70 mol% of the polyol involved the addition of only one molecule ofpolyhydroxyl-tertiary amine to each isocyanate group of thepolyisocyanate. This was confirmed by GPC analysis (major peak at Mn2840).

A clear coating composition was made by first forming components 1 and 2and then mixing these components together. Component 1 was prepared byfirst making up concentrate 1 as follows:

Concentrate 1 Ingredient Parts by weight Xylene 3.8 Ethyl acetate 2.0N,N-dimethyl dodecyl amine 0.32 Tinuvin ® 292 ((1,2,2,6,6-pentamethyl-0.58 4-piperidenyl)-sebacate) Tinuvin ® 328 (2-(2-hydroxy-3,5-ditertiary0.58 amyl phenyl)-2H-benzotriazole) Byk ® 325 (polysiloxane polyethercopolymer) 0.386 Dibutyl tin laurate 0.04 Toluene 2.94 Methyl ethylketone 5.88 Acetone 47.06 Acetic acid 0.164 Triethylenediamine 0.04Total 63.75

Concentrate 1 was then used to form component 1 having the followingcompositions:

Component 1, Case 1 Parts by Weight Concentrate 1 64 Acrylic polymer 1solution 100 Butyl acetate 26 Total 190

Component 1, Case 2 Parts by Weight Concentrate 1 64 Acrylic Polymer 1solution 95 Butyl acetate 26 Oligomer 1 solution 3.5 Total 188.5

Component 1, Case 3 Parts by Weight Concentrate 1 64 Acrylic Polymer 1solution 95 Butyl acetate 26 Oligomer 3 solution 4.2 Total 189.2

The polyisocyanate component (component 2) of the clear coatingcomposition was prepared as the following composition:

Component 2 Parts by Weight Desmodur ® N-3300 (1,6-hexamethylene 21Diisocyanate trimer, 100% solids) Butyl acetate 9 Methyl amyl isoketone5 Total 35

Clear coating compositions were made by mixing together components 1 and2 described above, followed by spraying them onto test panels and dryingat ambient temperature. The weight proportions of components 1 and 2were as follows:

Coating Composition Component 1 Component 2 1 190 35 2 188.5 35 3 189.235

Each of these compositions had a binder solids content of 37 wt % and aVOC content of 4.26 (0.51 kg solvent/l. of composition). Further detailsof each composition and their test results after application are shownin Table 1 (composition 3 is an example of the coating composition ofthe present invention).

TABLE 1 Coating Composition 1 2 3 Acrylic polymer 1 (wt % solids) 100 9595 Oligomer 1 (wt % solids) 0 5 0 Oligomer 3 (wt % solids) 0 0 5 NCO/OHequivalent ratio 1.2 1.13 1.08 (component 2/component1) Water spot (10 =best) After 30 min 5 4 7 After 45 min 8 7 9.5 After 60 min 9.5 9 10Persoz hardness (sec) After 3 hr 35 30 69

Composition 3 of the present invention exhibited improved earlyresistance to water spotting and much better early hardness than thecomparison compositions, being buffable in about 1-½ hr afterapplication of the film coating. The hardness after 24 hr was about thesame for all three compositions. The film coating of composition 3 wasalso dust-free faster than the film coatings from compositions 1 and 2,i.e. about 5 min for composition 3 as compared to about 10 min forcompositions 1 and 2.

Example 2

Oligomer 3 in Example 1 was made by reacting together triethoxylatedN-tallow-1,3-diaminopropane with IPDI trimer. In this Example 2,different polyhydroxy-tertiary amines are reacted with IPDI trimer toobtain the oligomer 4 series of polyols in solution (70 wt % solids)using the same procedure as described in Example 1 and the weightproportions of each ingredient present in the reaction were as follows:

Oligomer 4 Ethomeen ® IPDI Trimer Butyl Ac. −1 C-12-124 146 53 −2S-12-124 121 53 −3 O-12-124 120 53 −4 T-12-124 121 53 −5octadecyl-12-124 117 125 −6 * - 97 58.3 31.4 * The polyhydroxy-tertiaryamine used in composition 4-6 was a mixture of ingredients in thefollowing weight proportions: oligomer 1 (37)/oligomer 2 (30)/Ethomeen ®C-12(30)/IPDI trimer (58.3)/butyl acetate (31.4).

In this Table, C, S, 0 and T mean coco, soya, oley, and tallow,respectively, and “12” is not the carbon atom count as in Table A above,but instead has the following meaning: In “12”, the “1” indicates thenumber of —CH₂CH₂O— groups and the “2” indicates number of CH₂CH₂Obranches from the nitrogen atom. Thus, Ethomeen C-12 has the followingformula:

Component 1 in this Example is made using the following concentrate:

Concentrate 2 Ingredient Parts by weight Acrylic polymer 1 solution 95Butyl acetate 26 Ethyl acetate 2.0 N,N-dimethyl dodecyl amine 0.33Tinuvin ® 292 ((1,2,2,6,6-pentamethyl- 0.58 4-piperidenyl)-sebacate)Tinuvin ® 328 (2-(2-hydroxy-3,5-ditertiary 0.58 amylphenyl)-2H-benzotriazole) Byk ® 325 (described above) 0.19 Byk 333 ®(polysiloxane-modified polyester) 0.386 Dibutyl tin laurate 0.04 Toluene4.94 Methyl ethyl ketone 5.88 Acetone 47.06 Acetic acid 0.16Triethylenediamine 0.04 Total 183

Component 1 is made by mixing together concentrate 2 with oligomers 4 asfollows:

Component 1, Cases 1-4 and 6 Parts by Weight Concentrate 2 183 Oligomers4-1, 4-2, 4-3, 4-4, and 4-6 solution 4.2 Total 187.2

Component 1, Case 5 Parts by Weight Concentrate 2 183 Oligomer 4-5solution 5.3 Total 188.3

The polyisocyanate component (component 2) was prepared having thefollowing composition:

Component 2, Cases 1-6 Parts by Weight Desmodur ® N-3300 (as describedabove) 21 Butyl acetate 9 Methyl amyl isoketone 5 Total 35

To form the clear coating compositions each being 37 wt % solids,components 1 and 2 were mixed together in the following proportions:Compositions 1-4 and 6, 187.2/35, respectively, and Composition 5,188.3/35, respectively. The compositions had an NCO/OH equivalencybetween 1.08 and 1.12, and the VOC for each composition was less than4.3 (0.52 kg/l). The compositions were applied to test panels and driedat ambient temperature. Further details on composition and test resultsare shown in Table 2.

TABLE 2 Coating Composition 1 2 3 4 5 6 Acrylic polymer 1 95 95 95 95 9595 Oligomer 4-1 5 0 0 0 0 0 Oligomer 4-2 0 5 0 0 0 0 Oligomer 4-3 0 0 50 0 0 Oligomer 4-4 0 0 0 5 0 0 Oligomer 4-5 0 0 0 0 5 0 Oligomer 4-6 0 00 0 0 5 Water spot (10 = best) After 15 min 5 6 6 6 7 7 After 30 min 1010 10 10 10 10 Persoz hardness (sec) After 3 hr 70 65 67 63 73 61

All of the coating films formed from these compositions exhibitedoutstanding early freedom from water spot damage and hardness. The filmcoatings could all be buffed in about 1-½ hr and were dust free in lessthan 5 min.

Example 3

In this Example, the presence of polyol of the present invention in thecoating composition provided a film coating that could be buffed onehour after application (drying at ambient temperature).

In this Example, the hydroxy component of the coating composition hadthe following composition:

Component 1, Cases 7 and 8 Parts by Weight Ingredient Case 7 Case 8Xylene 8.29 6.27 Ethyl acetate 3.1 3.1 N,N-dimethyl dodecyl amine 0.270.25 Tinuvin ® 292 (as described above) 0.73 0.66 Tinuvin ® 328 (asdescribed above) 0.73 0.66 Byk ® 333 (as described above) 0.05 0.04Dibutyl tin laurate 0.08 0.07 Toluene 2.9 2.5 Methyl isobutyl ketone5.85 4.8 Acetone 24.3 21.9 Acetic acid 0.28 0.25 Methyl amyl ketone 9.17.0 Byk ® 358 (as described above) 0.3 0.26 Acrylic polymer 1 solution61.8 61.2 Oligomer 3 0 0.7 Butyl acetate 12.3 9.2 Triethylenediamine0.06 0.06 Totals 130.1 118.9

Component 2 had the following composition:

Parts by Weight Desmodur ® N-3000 (as described above) 62.6 Desmodur ®Z-4470 BA (as described above) 15.7 Butyl acetate 7.5 Methyl amylisoketone 14.2 Total 100

The following coating compositions were prepared by mixing togethercomponents 1 and 2:

Composition Component 1 - g Component 2 - g Using case 7 comp. 54 16Using case 8 comp. 56.6 13.4

These compositions contained the following:

Composition (wt %) Using Case 7 Comp. Using Case 8 Comp. Acrylic polymer1 100 98 Oligomer 3 0 2 IPDI trimer* 15 15 *The wt % IPDI trimer isbased on the total weight of polyisocyanate.

The case 8 composition is a composition of the present invention. Withinone hour after spraying this composition onto a test panel, followed byair drying, the resultant coating film was both buffable and wetsandable. This indicates that the coating film was very quicklydust-free (within 5 min), was water-spot free and had a Persoz hardnessof at least 35 sec. In comparison, the coating film using the case 7composition of component 1, was too soft to be buffed at one hour afterapplication, and was not ready for buffing until many hours afterapplication. Drying at ambient temperature was used for both coatingfilms.

Example 4

The following concentrate was prepared:

Concentrate 3 Ingredient Parts by Weight Ethyl acetate 2.4 Tinuvin ® 292(described above) 0.58 Tinuvin ® 328 (described above) 0.58 Byk ® 325(described above) 0.386 Dibutyl tin dilauurate 0.04 Toluene 2.94 Methylethyl ketone 5.88 Acetone 47.06 Acetic acid 0.164 Total 60

A clear coating compposiion was made by first forming components 1 and 2and then mixing these cxomponents together. Component 1 had thefolloweing compositions:

Component 1, Case 9 Parts by Weight Concentrate 3 60 Acrylic polymer 1solution 100 Butyl acetate 26 Total 186

Component 1, Case 10 Parts by Weight Concentrate 3 60 Acrylic polymer 1solution 95 Butyl Acetate 26 Oligomer 1 3.5 Total 184.5

Component 1, Case 11 Parts by Weight Concentrate 3 60 Acrylic polymer 1solution 95 Butyl acetate 26 Oligomer 3 4.2 Total 185.2

Component 2 had the following composition:

Component 2, Cases 9-11 Parts by Weight Desmodur ® 3300 (describedabove) 18.9 Desmodur ® 4470BA (described above) 3.0 Butyl Acetate 8.1Methyl amyl isoketone 5.0 Total 35

Components 1 and 2 were mixed together in the following proportions toform the clear coating composition (VOC content of 0.51 kg/l; 37 wt %solids):

Coating composition Amount of Component 1-g Amount of Component 2-g Case9  186 35 Case 10 184.5 35 Case 11 185.2 35

These coating compositions were then applied to test panels and dried atambient temperature. Further details of the composition and test resultsare presented in the following table:

TABLE 3 Ingredient Case 9 Case 10 Case 11 Acrylic polymer 1 (solids) 10095 95 Oligomer 1 (solids) 0 5 0 Oligomer 3 (solids) 0 0 5 IPDI Trimer(solids)* 10 10 10 NCO/OH 1.18 1.11 1.06 Water spot at ambienttemperature After 30 min 5 4 6 After 45 min 7 7 8 After 60 min 9 8 9.5Persoz hardness (sec) After 3 hr 32 48 70 *The wt % IPDI trimer is baseon the total weight of polyisocyanate making up component 2.

Composition Case 11 is the composition of the present invention. Thecoating film of this composition exhibits improved water spot resistanceas compared to the other compositions and greatly improved cure rate,achieving buffability is about 1-½ hr. The coating film of composition11 was dust free in about 5 min after application.

What is claimed is:
 1. A coating composition containing a film formingbinder and a volatile organic liquid carrier, wherein the bindercontains hydroxyl-containing acrylic polymer and polyol prepared byreacting together polyhydroxy-tertiary amine with organicpolyisocyanate, the polyhydroxyl-tertiary amine having at least twohydroxyl groups being bonded indirectly to a nitrogen atom of said aminethrough a chain containing at least two carbon atoms, essentially all ofthe isocyanate groups of said organic polyisocyanate being reacted withhydroxyl groups of said amine.
 2. The coating composition of claim 1wherein said binder constitutes component A of said composition andorganic polyisocyanate is present as component B, the ratio ofequivalents of isocyanate in (B) per equivalent of hydroxyl groups in(A) being in the range of 0.5/1 to 3.0/1, and an effective amount ofcatalyst to cure said composition is present as component C.
 3. Thecoating composition of claim 2 wherein an effective amount of saidpolyol in said component (A) is present to increase the curing rate ofsaid composition.
 4. The coating composition of claim 2 wherein theamount of said hydroxyl-containing acrylic polymer is 40-99 wt % and theamount of said polyol is 1-60 wt %, based on the total weight of (A). 5.The coating composition of claim 2 wherein said component (A) contains0-39 wt % of hydroxyl-terminated polyester, based on the total weight of(A).
 6. The coating composition of claim 2 wherein the composition is atwo-pack coating composition, comprising in the first pack, components Aand C, and in the second pack, component B, wherein the contents of eachpack are mixed together just prior to use.
 7. The coating composition ofclaim 2 wherein said organic polyisocyanate present as component (B)contains 0-30 wt % of the trimer of isophorone diisocyanate, based onthe total weight of component (B).
 8. The coating composition of claim 2wherein said polyhydroxyl-tertiary amine used in said polyol ofcomponent (A) contains two tertiary amine nitrogen atoms, each having atleast one hydroxyl group indirectly bonded thereto through a chaincontaining at least two carbon atoms.
 9. The coating composition ofclaim 2, wherein said polyhydroxyl-tertiary amine used in said polyol ofcomponent (A) has the formula

wherein R is alkylene or oxyalkyene containing 0 to 6 carbon atoms and Xand Y are independently R₁H, wherein R₁ is —(CH₂CH₂O)_(n)— or—(CH₂C(CH₃)HO)_(n)—, wherein n is an integer of 1-3, and A is R—X, R—Y,R₂ or Z, wherein R₂ is an alkyl group containing 1-20 carbon atoms and

wherein R₃ is an alkylene group containing 1 to 10 carbon atoms, withthe proviso that at least two hydroxyl groups are present.
 10. Thecoating composition of claim 9 wherein said organic polyisocyanate usedin said polyol of component (A) has the formula

wherein B is an aliphatic or aromatic nucleus of said organicpolyisocyanate and p is an integer of at least
 2. 11. The coatingcomposition of claim 10 including the polyol compound having the formula